Systems and methods for improved metal recovery using ammonia leaching

ABSTRACT

Systems and methods for basic leaching are provided. In various embodiments, a method is provided comprising leaching a slurry comprising a copper bearing material and an ammonia leach medium, adding copper powder to the slurry, separating the slurry into a pregnant leach solution and solids, and performing a solvent extraction on the pregnant leach solution to produce an loaded aqueous stream.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims priority toU.S. patent application Ser. No. 14/940,548 entitled “SYSTEMS ANDMETHODS FOR IMPROVED METAL RECOVERY USING AMMONIA LEACHING” which wasfiled on Nov. 13, 2015, now U.S. Pat. No. 10,006,133, issued Jun. 26,2018. The '548 applications is a continuation application of and claimspriority to U.S. patent application Ser. No. 13/804,009, entitled“SYSTEMS AND METHODS FOR IMPROVED METAL RECOVERY USING AMMONIALEACHING,” which was filed Mar. 14, 2013, now U.S. Pat. No. 9,187,803,issued Nov. 17, 2015. The aforementioned applications are herebyincorporated by reference herein in their entirety.

FIELD

The present disclosure relates, generally, to systems and methods forrecovering metal values from metal bearing materials, and morespecifically, to systems and methods for processing acid consuming ores.

BACKGROUND

Hydrometallurgical treatment of metal bearing materials, such as copperores, concentrates, and other metal bearing materials, has been wellestablished for many years. Typically, conventional hydrometallurgicalprocesses for copper recovery involve leaching metal bearing materialswith an acidic solution, either atmospherically or under conditions ofelevated temperature and pressure. The resultant process stream—thepregnant leach solution—is recovered, and a processing step such assolvent extraction is used to form a highly concentrated and relativelypure metal value containing aqueous phase. One or more metal values maythen be electrowon from this aqueous phase.

Certain ores consume a relatively high amount of acid during acidicleaching. Thus, highly acid consuming ores have conventionally been moreexpensive to process through acidic leaching. Highly acid consumingcopper containing ores include copper carbonates, such as azurite andmalachite, among other types of minerals.

Certain ores and/or flotation tailings contain a mix of oxides andsulfides of one or more metals associated with highly acid consuminggangue materials such as carbonates. These mixed materials may beproblematic in acid leaching because of the highly acid consuming natureof the gangue minerals and because sulfide minerals leach more slowlyand less completely than oxide minerals, causing low metal recovery andplant design complications.

Accordingly, processes that allow for metal recovery from highly acidconsuming ores without the need for acid leaching would be advantageous.

SUMMARY

Accordingly, the present invention provides systems and methods formetal value recovery. In various embodiments, a method is providedcomprising leaching a slurry comprising a copper bearing material and anammonia leach medium, adding copper powder to the slurry, separating theslurry into a pregnant leach solution and solids, and performing asolvent extraction on the pregnant leach solution to produce a loadedaqueous stream.

Further, various embodiments of the present invention provide a systemcomprising a wet grinding apparatus configured to grind a metal bearingmaterial, a basic leaching vessel configured to receive copper powderand the ground metal bearing material and produce a basic pregnant leachslurry, and a solvent extraction train configured to receive the liquidportion of the basic pregnant leach slurry.

Further areas of applicability will become apparent from the detaileddescription provided herein. It should be understood that thedescription and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present invention is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present invention, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements and wherein:

FIG. 1 is a flow diagram illustrating a process in accordance withvarious embodiments of the present invention;

FIG. 2 is a flow diagram illustrating a process having a wet grind, inaccordance with various embodiments of the present invention;

FIG. 3 is a flow diagram illustrating a process having an ammonia leach,in accordance with various embodiments of the present invention;

FIG. 4 is a flow diagram illustrating a process having a cobaltprecipitation, in accordance with various embodiments of the presentinvention;

FIG. 5 is a graph illustrating cobalt extraction varying in relation tothe ratio of moles of copper powder to moles of cobalt, in accordancewith various embodiments of the present invention;

FIG. 6 is a graph illustrating cobalt leaching kinetics in accordancewith various embodiments of the present invention;

FIG. 7 is a graph illustrating copper leaching kinetics in accordancewith various embodiments of the present invention; and

FIG. 8 is the graph of FIG. 7 having an expanded y axis in accordancewith various embodiments of the present invention.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present invention, its applications, or its uses.It should be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.The description of specific examples indicated in various embodiments ofthe present invention are intended for purposes of illustration only andare not intended to limit the scope of the invention disclosed herein.Moreover, recitation of multiple embodiments having stated features isnot intended to exclude other embodiments having additional features orother embodiments incorporating different combinations of the statedfeatures.

Furthermore, the detailed description of various embodiments hereinmakes reference to the accompanying drawing figures, which show variousembodiments by way of illustration. While the embodiments are describedin sufficient detail to enable those skilled in the art to practice theinvention, it should be understood that other embodiments may berealized and that logical and mechanical changes may be made withoutdeparting from the spirit and scope of the present invention. Thus, thedetailed description herein is presented for purposes of illustrationonly and not of limitation. For example, steps or functions recited indescriptions any method, system, or process, may be executed in anyorder and are not limited to the order presented. Moreover, any of thestep or functions thereof may be outsourced to or performed by one ormore third parties. Furthermore, any reference to singular includesplural embodiments, and any reference to more than one component mayinclude a singular embodiment.

The present invention relates, generally, to systems and methods forrecovering metal values from metal-bearing materials, and morespecifically, to systems and methods for metal recovery using basicleaching. These improved systems and methods disclosed herein achieve anadvancement in the art by providing a metal value recovery system thatavoids the use of acid leach media in connection with high acidconsuming metal bearing materials. Such technology tends to reduce thecost of metal recovery by, at least, eliminating acid costs associatedwith leaching a given ore body mass. Moreover, acid-free recovery ofmetal bearing materials often employs roasting technology. Roastingtends to consume significant energy, which may be expensive andenvironmentally unfriendly, particularly in areas where energy isexpensive to produce and/or transport. In addition, roasters addsignificant capital expenditures as well as increased operatingexpenditures due to maintenance and repair.

In particular, it has been discovered that leaching with a medium thatcomprises ammonia combined with various other features may be used toleach metal values from metal bearing materials such as ore.

There are several highly acid consuming metal bearing materials, and theselection of certain parameters over others may be influenced by themetal bearing material type and the metal that is sought in recovery. Invarious embodiments, metal bearing materials contain a mixture ofoxides, sulfides, and carbonates. In various embodiments, copper issought to be recovered, as well as cobalt. In that regard, in variousembodiments, a mixed ore comprising sulfides may be combined with aleach in basic media to yield a metal value containing material that issuitable for use in a conditioning process, such as solvent extraction(sometimes referred to as solution extraction or liquid ion exchange).

Moreover, where both copper and cobalt are sought from a metal bearingmaterial, the oxidation state of copper and/or cobalt may need to beadjusted. For example, in certain forms, cobalt II is soluble in ammoniawhile cobalt III is not. Thus, during leaching, it has been found thatuse of various reagents tends to reduce, and thereby solubilize cobaltII, thereby allowing cobalt II to be liberated from the metal bearingmaterial and subject to further metal recovery operations. The reductionof, for example, cobalt, during leaching enhances efficiency, asseparate, pre-leaching operations need not be employed to reduce cobaltprior to leach. This results in a savings in both capital expenditureand operating expenditure. Reaction kinetics of cobalt recovery may alsobe improved using various reagents. In various embodiments, copperpowder may be used to effect reduction of cobalt, thus improving cobaltrecovery.

With reference to FIG. 1, metal recovery 100, in accordance with variousembodiments, is illustrated. Metal recovery 100 allows for metal valuesto be recovered from a basic leach without an acid leach. Metal recovery100 includes ore 102, which contains one or more metal values.

Ore 102 may comprise any metal bearing material, such as an ore, acombination of ores, a concentrate, a process residue, a flotationtailings product, an impure metal salt, combinations thereof, or anyother material from which metal values may be recovered. Metal valuessuch as, for example, copper, gold, silver, zinc, platinum group metals,nickel, cobalt, molybdenum, rhenium, uranium, rare earth metals, and thelike may be recovered from ore 102 in accordance with variousembodiments of the present invention. Various aspects and embodiments ofthe present invention, however, prove especially advantageous inconnection with the recovery of copper from highly acid consuming oresthat include copper carbonates, such as azurite and malachite, amongother highly acid consuming ores. In various embodiments, ore 102comprises at least one or more sulfides, carbonates, and oxides. Highlyacid consuming ores may comprise any metal bearing material thatrequires a high ratio or acid to metal bearing material volume to leacha commercially significant proportion of the metal values in the metalbearing material. In various embodiments, ore 102 comprises at leastcopper and cobalt and/or compounds comprised of copper and/or cobalt.

Ore 102 may be prepared in preparation 104. Preparation 104 may includeany form of preparation for ore 102 prior to reactive process 106. Invarious embodiments, preparation 104 is omitted, although variousadvantages may be derived through the use of preparation 104. Metalbearing materials may be prepared in a variety of ways. Ores may bedried, crushed, pulverized, finely ground, or undergo any combinationthereof. Ores may be concentrated to form a metal bearing concentrate. Avariety of acceptable techniques and devices for reducing the particlesize of the ore 102 are currently available, such as crushers, ballmills, tower mills, ultrafine grinding mills, attrition mills, stirredmills, horizontal mills and the like, and additional techniques maylater be developed that may achieve the desired result of increasing thesurface area of and exposing mineral surfaces within the material to beprocessed. In accordance with various embodiments, ore 102 may beprepared in preparation 104 by controlled wet grinding. Wet grindingtends to reduce capital expenditure and operating expenditures whencompared with dry grinding. For example, a uniform, particle sizedistribution may be achieved. In accordance with one aspect of thepresent disclosure, a particle size distribution of approximately 80%particle distribution passing size (P₈₀) of about 75 microns may beused, as well as a particle size distribution of approximately 98%particle distribution passing size (P₉₈) of about 100 to about 200microns. In accordance with one aspect of the present disclosure, aparticle size distribution of approximately 80% particle distributionpassing size (P₈₀) of about 74 microns may be used.

However, in various embodiments, a uniform, ultra-fine particle sizedistribution is not necessary. For example, in various embodiments, aparticle size distribution of approximately 80% particle distributionpassing size (P₈₀) of about 100 microns may be used, and in variousembodiments a particle size distribution of approximately 98% particledistribution passing size (P₉₈) of about 100 microns may be used. Invarious embodiments, preparation 104 does not include controlledgrinding, but does include crushing and grinding to produce largerand/or less uniform particle sizes. For example, preparation 104 maycomprise screening ore through a grizzly or other analogous device withabout 250 mm openings. Further, preparation 104 may also include a milloperation. Particles having a size of less than about 250 mm can bereceived by mill operation which then reduces the received particles toa particle size distribution suitable for downstream processing. Forexample, the mill operation may provide particles having about 80%particle distribution passing size (P₈₀) of 100 microns. Other particlesizes described herein may also be useful. For example, in variousembodiments, ore 102 may be ground to about 80% particle distributionpassing size (P₈₀) of between about 50 microns to about 500 microns andof between about 75 microns and 400 microns. Preparation 104 yields aprepared ore that may be subject to reactive process 106.

In accordance with various embodiments, reactive process 106 maycomprise any type of reactive process that is capable of yielding one ormore metal values in the prepared ore in a condition to be subjected tolater metal recovery steps. For example, in various embodiments,reactive process 106 comprises a leaching operation such as a basicleaching operation. In various embodiments, reactive process 106 yieldsa metal value bearing slurry.

Reactive process 106 may receive reducing agent 112. Reducing agent 112may comprise any substance capable of acting as a reducing agent. Forexample, reducing agent 112 may comprise sulfur dioxide and/or copperpowder.

Reducing agent 112 may reduce one or more metal values during reactiveprocess 106. For example, reducing agent 112 may reduce copper and/orcobalt during reactive process 106. While reducing agent 112 maycomprise any reagent that is capable of reducing copper and/or cobalt,reducing agent 112 may be selected based upon, among other factors, costand efficacy. As described herein, certain reducing agents may causeunexpected improvements in leaching kinetics.

The metal value bearing slurry may be processed by a solid liquid phaseseparation. A solid liquid phase separation may be accomplished in anysuitable manner, including use of filtration systems, counter-currentdecantation (CCD) circuits, thickeners, and the like. In variousembodiments, a solid liquid phase separation may comprise furtherconditioning processes such as, for example, filtration, to remove finesolid particles. A variety of factors, such as the process materialbalance, environmental regulations, residue composition, economicconsiderations, and the like, may affect the decision whether to employa CCD circuit, one thickener or multiple thickeners, one filter ormultiple filters, and/or any other suitable device or combination ofdevices in a solid liquid separation apparatus. The solid liquidseparation may separate metal value bearing slurry into a liquid portionand a solid portion. The liquid portion may be sent to solventextraction 108.

Solvent extraction 108 may comprise any solvent extraction process. Invarious embodiments, solvent extraction 108 comprises a liquid-liquidextraction. During solvent extraction 108, metal values from the liquidportion of the metal value bearing slurry may be loaded selectively intoan organic phase in an extraction phase, wherein the organic phasecomprises an extracting agent to aid in transporting the metal values tothe organic phase. The extraction phase may produce an aqueousraffinate. The aqueous raffinate from the extraction phase may includemetal values, such as copper and/or cobalt, and thus may be treated torecovery such metal values, among others.

After the extraction phase, one or more scrub or wash stages may beemployed. In various embodiments, one or more scrub stages are employed.For example, carbon dioxide may be dissolved in water to form carbonicacid. Carbonic acid may be mixed with the organic phase to facilitatethe removal of entrained and extracted ammonia. As a weak acid, carbonicacid may neutralize entrained and extracted ammonia.

In various embodiments, one or more wash stages are employed. The washstage may be used to purge various impurities, such as sulfates, fromthe organic phase, for example, by washing with an aqueous solution.

The organic phase, whether directly from the extraction stage or afterone or more scrub/wash stages, may be then subjected to a solventstripping phase, wherein the metal values are transferred to an aqueousphase. For example, more acidic conditions may shift the equilibriumconditions to cause the metal values to migrate to the aqueous phase.Barren electrolyte from an electrowinning process may be used as astripping medium. Metal value containing liquid from solvent extraction108 may be referred to as a loaded aqueous stream.

The loaded aqueous stream from solvent extraction 108 may be subject tofurther processing 110, such as electrowinning, to yield metal value114.

With reference to FIG. 2, metal recovery process 200 is illustrated.Metal recovery process 200 contains certain steps found in metalrecovery process 100.

In accordance with various embodiments, wet grind 202 comprises a wetgrind of ore 102. A wet grind may be accomplished through any grindingmeans described herein or otherwise. In various embodiments, wetgrinding comprises sending coarse crushed ore to a semi-autogenousgrinding mill followed by wet ball mill grinding in a circuit closedwith a size classifier.

In accordance with various aspects, basic leach 204 receives the wetground ore from wet grind 202 and subjects the same to leaching in basicmedia. Basic media may comprise any media that has a pH of greater than7. Basic media may include an aqueous solution of ammonia, ammoniumand/or ammonium containing compounds such as ammonium carbonate,ammonium sulfate, hypochlorite solutions (e.g., sodium hypochlorite andcalcium, hypochlorite), peroxide solutions, percarbonate solutions,perborate solutions and combinations thereof. In various embodiments,ammonia alone or ammonia and a carbonate solution is used as basicmedia.

The basic media tends to liberate metal values from the wet ground ore.Basic leach 204 yields a metal value bearing slurry that may beprocessed by a solid liquid phase separation as described herein.

Electrowinning 206 may comprise any process that uses electrical energyto obtain a metal value. Metal value bearing solution from solventextraction 108 may be introduced into an electowinning cell inelectrowinning 206. Electrical energy may be applied to cause an ionicform of a metal value to transform into a non-ionic form.

With reference to FIG. 3, metal recovery process 300 is illustrated.Metal recovery process 300 contains certain steps found in metalrecovery process 200.

Ammonia leach 302 receives the wet ground ore from wet grind 202 andsubjects the same to leaching in media containing ammonia and/orammonium.

In accordance with various aspects, ammonia leach 302 comprises anagitated tank leach. Ammonia leach 302 may comprise an agitated tankleach that is performed at constant or varying basic pH levels. Basic pHlevels may range from about 7 to about 14. Ammonia leach 302 isperformed using basic media containing ammonia. For example, the basicmedia used in ammonia leach 302 may include an aqueous solution ofammonia. One or more metal values from the reduced metal bearingmaterial may be absorbed into the basic media. Basic media in liquidform that contains metal values may be referred to as a pregnant leachsolution.

Leach solutions may contain recycled solutions from upstream processesand recovered lixiviant from various processing steps. Fresh lixiviantmay also be added. Leaching may occur in several tanks, eitherco-currently or counter-currently depending on the leach characteristicsand kinetics. Preferably, the duration of leaching in accordance withvarious aspects of the present invention ranges from about 2 hours toabout 8 hours. More preferably, the duration ranges from about 4 hoursto about 7 hours.

While not wishing to be bound by theory, it is believed that the use ofammonia may be especially advantageous in leaching operations includingsulfide ores, for example copper containing sulfide ores. Air, ammonia,and sulfur dioxide (SO₂) may react with sulfide ores to yield ammoniumsulfite and sulfides. Ammonium sulfite and/or sulfides may undergoanother oxidizing reaction to yield thiosulfate and sulfide. Yet anotherreaction may occur to yield thionate from thiosulfate. Thiosulfate maybe regenerated by the addition of ammonium hydrosulfide.

Copper powder 304 is added to ammonia leach 302 as a reducing agent.Copper powder 304 acts to reduce cobalt III to cobalt II. Unexpectedly,copper powder 304 also improves the kinetics of cobalt recovery, asdescribed herein.

While not wishing to be bound by theory, it is believed that theaddition of copper powder reduces cobalt III to cobalt II. Cobalt II issoluble in basic media, such as ammonia, and may enter the basic mediasolution. Copper powder is an excellent source of copper metal, as ithas a large surface area and, when used in connection with or proximityto a copper recovery operation, copper powder may be produced on site,reducing procurement and transportation costs.

More particularly, and again not wishing to be bound by theory, acuprous-cupric couple may be used to reduce cobalt found in heterogenite(Co₂O₃). Copper metal reacts with a cupric complex to form a cuprouscomplex:Cu⁰+Cu(NH₃)₄ ²⁺+4NH₃→2Cu(NH₃)₄ ⁺

The cuprous complex may then react with the cobalt in heterogenite andthe reduced cobalt may become solubilized as an ammonia complex:Co₂O₃+2Cu(NH₃)₄ ⁺+6NH₄ ⁺+6NH₃→2Co(NH₃)₆ ²⁺+2Cu(NH₃)₄ ²⁺+3H₂O

Combining these two reactions gives an overall reaction:Co₂O₃+Cu⁰+6NH₄ ⁺+10NH₃→2Co(NH₃)₆ ²⁺+Cu(NH₃)₄ ²⁺+3H₂O

Based on the overall reaction, one mole of copper powder is required tosolubilize two moles of cobalt in heterogenite, giving a stoichiometricCu/Co molar ratio of 0.5.

However, it has been found that in practice, a greater ratio isadvantageous to offset other factors that may be present in the reactionenvironment. For example, the presence of oxygen may oxidize the cuprouscomplex to form the cupric complex. Also, the presence of iron in theform of ferric oxides may react similarly to heterogenite, oxidizing thecuprous complex to the cupric complex. Manganese in the form of MnO₂ mayalso oxidize the cuprous complex. These factors, among others, may bemitigated in various embodiments by controlling or limiting the presenceof oxygen, iron compounds, and/or manganese compounds, among others.These factors may be overcome by adding additional copper powder so thatthe Cu/Co molar ratio is above that suggested by stoichiometry, namely0.5. For example, a Cu/Co molar ratio of 4 to 12 may be advantageous, asdescribed herein below.

Copper powder 304 may comprise dendritic copper powder, molten sprayedcopper powder, and/or other forms of copper powder. Molten sprayedcopper powder comprises copper powder produced by spraying molten copperinto fine droplets. Dendritic copper powder comprises copper powderproduced by an electric refining process such as electrolysis. Dendriticcopper powder may have a mean particle size on the order of from about40 microns to about 150 microns, though dendritic copper powder of othermean particle sizes is also contemplated. Dendritic copper powder may beproduced directly from an electrolysis process or may be further ground,milled, or otherwise processed after initial production in anelectrolysis process. It has been found that effective use of moltensprayed copper powder is associated with a ratio of about 8 moles ofmolten sprayed copper powder to 1 mole of cobalt. It has been found thateffective use of dendritic copper powder is associated with a ratio ofabout 1 moles of dendritic copper powder to 1 mole of cobalt.

While not wishing to be bound by theory, it is believed that the largersurface area of dendritic copper powder as compared to molten sprayedcopper powder renders dendritic copper powder more chemically active.Stated another way, it is believed that the high surface area ofdendritic copper powder allows the dendritic copper powder to have agreater reductive capacity per mole than molten sprayed copper powder.

Moreover, while molten sprayed copper powder is available commercially,dendritic copper powder may be produced from an electrowinningoperation. Electrowinning operations typically occur in close proximityto basic leaching processes such as that of the present disclosure, sotransportation cost of reagent (the dendritic copper powder) tends to bereduced.

The pregnant leach solution may be present with solids in ammonia leach302. Together, the pregnant leach solution and solids of ammonia leach302 may be referred to as a metal bearing slurry.

The slurry from ammonia leach 302 is subject to a solid liquid phaseseparation as described herein, such a CCD circuit. Liquids from thesolid liquid phase separation 112 may be forwarded to solvent extraction108.

The loaded aqueous stream from solvent extraction 108 may be subject tofurther processing, such as electrowinning 206, to yield metal value114.

In electrowinning 206, in accordance with various embodiments, the anodeis configured to enable the electrolyte to flow through it. As usedherein, the term “flow-through anode” refers to an anode so configured.

Any now known or hereafter devised flow-through anode may be utilized inaccordance with various aspects of the present invention. Possibleconfigurations include, but are not limited to, metal wool or fabric, anexpanded porous metal structure, metal mesh, multiple metal strips,multiple metal wires or rods, perforated metal sheets, and the like, orcombinations thereof. Moreover, suitable anode configurations are notlimited to planar configurations, but may include any suitablemultiplanar geometric configuration.

While, in various embodiments, anodes may be lead-containing (e.g.,Pb—Sn—Ca), preferably, the anode is formed of one of the so-called“valve” metals, including titanium (Ti), tantalum (Ta), zirconium (Zr),or niobium (Nb). The anode may also be formed of other metals, such asnickel, or a metal alloy, intermetallic mixture, or a ceramic or cermetcontaining one or more valve metals. For example, titanium may bealloyed with nickel (Ni), cobalt (Co), iron (Fe), manganese (Mn), orcopper (Cu) to form a suitable anode. Preferably, the anode comprisestitanium, because, among other things, titanium is rugged andcorrosion-resistant. Titanium anodes, for example, when used inaccordance with various aspects of embodiments of the present invention,potentially have useful lives of up to fifteen years or more. Titaniumanodes may comprise titanium-clad anodes. Titanium-clad anodes comprisea metal, such as copper, clad in titanium,

The anode may also comprise any electrochemically active coating.Exemplary coatings include those that comprise platinum, ruthenium,tantalum, iridium, other Group VIII metals, oxides of the same, andmixtures of the same. Ruthenium oxide, tantalum oxide, and iridium oxideare preferred for use as the electrochemically active coating ontitanium anodes when such anodes are employed in connection with variousembodiments. In accordance with one embodiment of the invention, theanode is formed of a titanium metal mesh coated with an iridium oxideand/or tantalum oxide-based coating. In such embodiments, the iridiumoxide and/or tantalum oxide-based coating may be comprised of multiplelayers of iridium oxide and/or tantalum oxide. The multiple layers maycomprise iridium oxide and/or tantalum oxide in an amorphous state or acrystalline state. In another embodiment of the invention, the anode isformed of a titanium mesh coated with a rutheium-based oxide coating.Anodes suitable for use in accordance with various embodiments of theinvention are available from a variety of suppliers.

In various embodiments, copper electrowinning operations use either acopper starter sheet or a stainless steel or titanium “blank” as thecathode. In accordance with one aspect of an exemplary embodiment, thecathode is configured as a metal sheet. The cathode may be formed ofcopper, copper alloy, stainless steel, titanium, or another metal orcombination of metals and/or other materials. The cathode is typicallysuspended from the top of the electrochemical cell such that a portionof the cathode is immersed in the electrolyte within the cell and aportion (generally a relatively small portion, less than about twentypercent (20%) of the total surface area of the cathode) remains outsidethe electrolyte bath. The total surface area of the portion of thecathode that is immersed in the electrolyte during operation of theelectrochemical cell is referred to herein, and generally in theliterature, as the “active” surface area of the cathode. This is theportion of the cathode onto which copper is plated duringelectrowinning.

In accordance with various embodiments of the present invention, thecathode may be configured in any manner now known or hereafter devisedby the skilled artisan.

In accordance with various embodiments, the copper concentration in theelectrolyte for electrowinning is advantageously maintained at a levelof from about 20 to about 60 grams of copper per liter of electrolyte.Preferably, the copper concentration is maintained at a level of fromabout 30 to about 50 g/L, and more preferably, from about 40 to about 45g/L. However, various aspects of the present invention may bebeneficially applied to processes employing copper concentrations aboveand/or below these levels.

With reference to FIG. 4, metal recovery process 400 is illustrated.Metal recovery process 400 contains certain steps found in metalrecovery process 300.

During ammonia leach 302, copper powder 304 is added with sulfur dioxide(SO₂) 406 and air 408. Air 408 and SO₂ 406 may be added in gaseous form.Air and (SO₂) may be added into a leaching vessel at any point of theleaching vessel. For example, air 408 and SO₂ 406 may enter the leachingvessel near the bottom of the leaching vessel and allowed to “bubble” tothe top. Air 408 and SO₂ 406 may also be added near the top of theleaching vessel. Air 408 and SO₂ 406 may be added at any suitablepartial pressure. Air and SO₂ may be added at any point during thekinetically controlled leach reaction. For example, air and SO₂ may beadded separately at different times. Additions of gaseous reactants mayoccur within the first hour of the leach cycle, after one or more hourshave elapsed, or within the last hour or the leach cycle.

Raffinate from solvent extraction 108 may be sent to cobaltprecipitation 402 where ammonium hydrosulfide 404 may be added. Whilenot wishing to be bound by theory, it is believed that ammoniumhydrosulfide 404 may act to regenerate thiosulfate, as described above.Ammonium hydrosulfide 404 may also act to precipitate cobalt as cobaltsulfide. In various embodiments, cobalt may be precipitated using anadditional precipitating agent. Cobalt containing solids may then beforwarded to further processing for cobalt recovery. The liquid portionof cobalt precipitation 402, which contains ammonia, may be sent toammonia leach 302.

Countercurrent decantation 410 is shown as a solid liquid phaseseparation that receives slurry from ammonia leach 302 and separates theslurry into a solid portion and a liquid portion.

EXAMPLE

Tests were conducted in accordance with various embodiments disclosedherein. An ammonia leach is performed on an ore containing heterogeniteand copper bearing minerals, including copper sulfides. Copper powder isadded, which is believed to reduce the cobalt found in heterogenite.Several test processes are run with varying amounts of copper powderadded to the ammonia leach. FIG. 5 illustrates the results. Cobaltextraction percentage is shown in the y axis. Copper powder, asexpressed as moles of copper powder to moles of cobalt, is shown in thex axis. As predicted by the overall reaction, there is a stoichiometricCu/Co molar ratio of 0.5. However, as shown in FIG. 5. cobalt extractionpercentage is approximately 40% at Cu/Co molar ratio of 0.5. As shown, aCu/Co molar ratio of approximately 5.5 yields approximately 80% cobaltextraction and a Cu/Co molar ratio of approximately 10 yieldsapproximately 90% cobalt extraction. Thus, the Cu/Co molar ratio may beadjusted in accordance with the desired cobalt extraction rate. Thus, invarious embodiments, the Cu/Co molar ratio of approximately 0.5 orgreater is used, for example 0.5 to 10, 0.5 to 10, and a 0.5 to 6. Froma mass perspective, it has been found that between 2.5 kg of copperpowder per ton of ore to 5 kg or greater of copper powder per ton isbeneficial.

Unexpectedly, the leaching kinetics of cobalt are found to be enhancedby the addition of copper powder. FIG. 6 shows the results of threetests that involve the use of no copper powder, 2.5 kg of copper powderper ton of ore, and 5 kg of copper powder per ton of ore. The percentageof residue cobalt is given on the y axis and the retention time, inhours, is given on the x axis.

As shown in FIG. 6, after two hours, the percentage of residue cobalt ismuch lower in the tests involving the addition of copper powder. At 2hours, the test having no added copper powder had a percentage ofresidue cobalt of about 0.12%, whereas the tests having a copper powderaddition have a percentage of residue cobalt of about 0.04%. Even after6 hours, the test having no added copper powder does not drop below 0.1%residue cobalt, whereas at six hours, the tests having a copper powderaddition have a percentage of residue cobalt of above about 0.02%.

The leaching kinetics of copper are found to be relatively undisturbedby the addition of copper powder. FIGS. 7 and 8 show copper leachingkinetics. Percentage of residue copper percentage is displayed on the yaxis and retention time on the x axis. FIG. 7 includes a y axis from 0%to 4.5%. As shown, copper leaching kinetics are nearly the same for eachtest.

In FIG. 8, the y axis is “expanded” into smaller increments to betterillustrate the differences between the three tests. In subsequentexperimentation, it has been found that the introduction of air may actto oxidize residual copper metal, which may lead to even less variationin copper kinetics.

It is believed that the disclosure set forth above encompasses at leastone distinct invention with independent utility. While the invention hasbeen disclosed in the exemplary forms, the specific embodiments thereofas disclosed and illustrated herein are not to be considered in alimiting sense as numerous variations are possible. Equivalent changes,modifications and variations of various embodiments, materials,compositions and methods may be made within the scope of the presentinvention, with substantially similar results. The subject matter of theinventions includes all novel and non-obvious combinations andsubcombinations of the various elements, features, functions and/orproperties disclosed herein.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element orcombination of elements that may cause any benefit, advantage, orsolution to occur or become more pronounced are not to be construed ascritical, required, or essential features or elements of any or all theclaims of the invention. Many changes and modifications within the scopeof the instant invention may be made without departing from the spiritthereof, and the invention includes all such modifications.Corresponding structures, materials, acts, and equivalents of allelements in the claims below are intended to include any structure,material, or acts for performing the functions in combination with otherclaim elements as specifically claimed. The scope of the inventionshould be determined by the appended claims and their legal equivalents,rather than by the examples given above.

What is claimed is:
 1. A method comprising: leaching a slurry comprisinga metal bearing material and an ammonia leach medium, wherein the metalbearing material comprises copper and cobalt; adding a reducing agent tothe slurry, wherein the reducing agent comprises a dendritic copperpowder, and wherein the reducing agent is added to the slurry such thata stoichiometric ratio of copper to cobalt is greater than 0.5; andseparating the slurry into a pregnant leach solution and solids; andperforming a solvent extraction on the pregnant leach solution toproduce a loaded aqueous stream.
 2. The method of claim 1, wherein thestoichiometric ratio of copper to cobalt is between about 4 and about12.
 3. The method of claim 2, wherein the stoichiometric ratio of copperto cobalt is about
 8. 4. The method of claim 1, further comprising:producing a cobalt precipitate from a raffinate produced by the solventextraction; and subjecting the cobalt precipitate to a metal recoveryprocess.
 5. The method of claim 4, further comprising adding ammoniumhydrosulfide to the raffinate produced by the solvent extraction.
 6. Themethod of claim 1, subjecting the loaded aqueous stream toelectrowinning.
 7. The method of claim 1, further comprising wetgrinding the metal bearing material prior to the leaching.
 8. The methodof claim 1, further comprising adding sulfur dioxide gas to the slurry.9. The method of claim 8, further comprising adding air to the slurry.10. The method of claim 1, wherein the solvent extraction comprisessubjecting the pregnant leach solution to a copper specific extractingreagent.
 11. The method of claim 1, wherein the solvent extractioncomprises scrubbing an organic phase with a weak acid.
 12. The method ofclaim 11, wherein the weak acid is carbonic acid.
 13. The method ofclaim 12, wherein the carbonic acid is added through dissolving carbondioxide in water.
 14. The method of claim 1, wherein the leaching isperformed in an anoxic environment.